The present invention relates to a cationic paint composition and more specifically relates to a cationic electrodeposition paint composition capable of forming a cured coating film excellent in performances such as throwing power, rust preventive steel plate aptitude etc.
Cationic electrodeposition paint composition has been used mainly for undercoating of a car body as an electrodeposition paint and other wide range of applications and products having various properties have been developed up to now. For example, there has been proposed a cationic electrodeposition paint composition which contains a base resin containing an epoxy resin, which contains amino group and/or quaternary ammonium group as water-solubilizing group and is internally plasticized with a plasticizer such as polyamide, polyester, polyether etc., and is excellent in corrosion resistance and good in rust preventive steel plate aptitude and adhesion. In such a cationic electrodeposition paint composition there are compounded lead compounds or chromium compounds, for example, lead chromate, basic lead silicate, strontium chromate etc. as anticorrosive pigment. Recently, however, the use of such harmful compounds as lead compounds or chromium compounds is restricted in terms of pollution problems and the development of a cationic paint composition, excellent in corrosion resistance without compounding lead compounds or chromium compounds, has been strongly desired.
As an epoxy resin which is internally plasticized with a plasticizer tends to deteriorate the corrosion resistance of the coating film, it may be considered to improve the corrosion resistance by using as base resin an epoxy resin without containing a plasticizing modifier. There is, however, a problem that a paint composition using a non-plasticized epoxy resin has a lower rust preventive steel plate aptitude.
Moreover, it has been proposed to compound to an epoxy resin a plasticizer which does not deteriorate the corrosion resistance of the coating film, for example, polyol resin such as polyester polyol, polyether polyol, polyurethane polyol, acrylpolyol etc.; polyolefin such as polybutadiene, polyethylene etc. There are problems, however, that these materials are not compatible enough with epoxy resin and are not only poorly effective to improve the rust preventive steel plate aptitude but also deteriorate the corrosion resistance of the coating film if compounded much.
On the other hand, a throwing power is required to a cationic electrodeposition paint composition as a rust preventive countermeasure for baggy parts of a car body (locker, side-sill, pillar) etc. Particularly recently a higher throwing power is required to a cationic electrodeposition paint composition because of more complicated body structure, such as putting reinforcement to the locker part and in the side-sill from levelling up of car safety level. Therefore it has been desired to develop a cationic electrodeposition paint composition having a high throwing power, excellent in corrosion resistance and rust preventive steel plate aptitude.
The present inventors repeated intensive research works to respond to the above-mentioned requirements. As a result, this time, they have found out that a cationic electrodeposition paint composition having not only a high throwing power but also excellent in rust preventive steel plate aptitude and corrosion resistance by compounding a certain specific kind of a polyol-modified amino group-containing epoxy resin in a cationic electrodeposition paint.
Thus, according to the present invention there is provided a cationic paint composition containing as resin component a polyol-modified amino group-containing epoxy resin obtained by reacting
(a) an epoxy resin with an epoxy equivalent of 180-2,500 with
(b) an acid compound selected from the group consisting of the phenols of the following formula (1) and the carboxylic acids of the following formula (2), 
xe2x80x83wherein,
X represents a hydrogen atom or a hydrocarbon group with a carbon atom number 1-15 which may have optionally substituents selected from the group consisting of xe2x80x94OH, xe2x80x94OR, xe2x80x94SH and xe2x80x94SR,
Y represents a hydrocarbon group with a carbon atom number 1-15 which may have optionally substituents selected from the group consisting of xe2x80x94OH, xe2x80x94OR, xe2x80x94SH and xe2x80x94SR,
wherein R represents an alkyl group.
(c) a polyol compound obtained from a compound (c1) containing a plurality of active hydrogen groups by adding a caprolactone (c2) and
(d) an amino group-containing compound.
Then, the cationic paint composition provided by the present invention will be described in more detail.
(a) Epoxy resin:
As an epoxy resin (a) to be the main skeleton of the polyol-modified amino group-containing epoxy resin according to the present invention it is suitable to have an epoxy equivalent in the range of 180-2,500, preferably 200-2,000 and more preferably 400-1,500 and a number-average molecular weight of generally at least 200, preferably in the range of 400-4,000 and more preferably 800-2,500. If the epoxy equivalent of the epoxy resin is less than 180, the corrosion resistance and throwing power of the formed cationic paint composition is poor. If, on the other hand, it is more than 2,500, the rust preventive steel plate (zinc-plated steel plate) aptitude is remarkably deteriorated,
As such an epoxy resin (a), a product obtained by reacting a polyphenol compound with an epihalohydrin, for example, epichlorohydrin, is preferable from a viewpoint of corrosion resistance etc. of the coating film.
As a polyphenol compound usable for the formation of said polyepoxide compound there can be mentioned, for example, bis(4-hydroxyphenyl)-2,2-propane (bisphenol A), 4,4-dihydroxybenzophenone, bis(4-hydroxyphenyl)methane (bisphenol F), bis(4-hydroxy-phenyl)-1,1-ethane, bis(4-hydroxyphenyl)-1,1-isobutane, bis(4-hydroxy-tert-butyl-phenyl)-2,2-propane, bis(2-hydroxynaphthyl)-methane, tetra(4-hydroxyphenyl)-1,1,2,2-ethane, 4,4-dihydroxy-diphenylsulfone, phenol novolac, cresol novolac etc.
As an epoxy resin obtained by the reaction of polyphenol compound and epichlorohydrin, above all, a product derived from bisphenol A and illustrated by the following formula 
wherein n=1-3 is preferable.
As such an epoxy resin available on the market, there can be mentioned, for example, products sold by Japan Epoxy Resin Co., Ltd. under the trade name of Epicote 828EL, 1002, 1004 and 1007.
(b) Acid compound:
Acid compound to be reacted with the above-mentioned epoxy resin (a) according to the present invention is at least one kind of compound selected from the group consisting of the phenols illustrated by the following formula (1) 
wherein
X represents a hydrogen atom or a hydrocarbon group with a carbon atom number 1-15 which may have optionally substituents selected from the group consisting of xe2x80x94OH, xe2x80x94OR, xe2x80x94SH and xe2x80x94SR, wherein R represents an alkyl group, and
the carboxylic acids illustrated by the following formula (2) 
wherein
Y represents a hydrocarbon group with a carbon atom number 1-15 which may have optionally substituents selected from the group consisting of xe2x80x94OH, xe2x80x94OR, xe2x80x94SH and xe2x80x94SR, wherein R represents an alkyl group.
In the above-mentioned formula (1) the hydrocarbon group with a carbon atom number 1-15 represented by X can be straight chain, branched chain or cyclic and, above all, alkyl groups with a carbon atom number 1-15, particularly 1-12, for example, methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl, nonyl etc. are preferable. These groups may be substituted optionally with a group selected from the group consisting of hydroxyl group (xe2x80x94OH), alkoxy group (xe2x80x94OR), mercapto group (xe2x80x94SH) and alkylthio group (xe2x80x94SR).
As specific examples of the phenols of the above-mentioned formula (1) there can be mentioned, for example, phenol, cresol, ethylphenol, p-tert-butylphenol, nonylphenol etc. Particularly alkyl phenols are preferable.
In the above-mentioned formula (2) the hydrocarbon group with a carbon atom number 1-15 represented by Y can be straight chain, branched chain or cyclic and specifically includes, for example, alkyl groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, nonyl etc.; alkenyl groups such as vinyl, oleyl etc.; aryl groups such as phenyl. These groups may be substituted optionally with at least one, preferably 1-3 groups selected from the group consisting of hydroxyl group, alkoxy group, mercapto group and alkylthio group. As a hydrocarbon group substituted with such a group there can be mentioned, for example, 1-hydroxyethyl, 1,1-dimethylolethyl, 1,1-di-methylolpropyl, 3,4,5-trihydroxyphenyl etc.
As carboxylic acids of the above-mentioned formula (2) there can be mentioned, for example, acetic acid, propionic acid, butyric acid, valeric acid, acrylic acid, oleic acid, glycolic acid, glyceric acid, lactic acid, dimethylolpropionic acid, dimethylolbutyric acid, dimethylolvaleric acid, benzoic acid, gallic acid etc. Above all, acetic acid, propionic acid, butyric acid, oleic acid, dimethylolpropionic acid, dimethylolbutyric acid, dimethylolvaleric acid and benzoic acid are preferable.
(c) Polyol compound:
In the present invention a polyol compound (c) is useful to internal plasticization of the aforementioned epoxy resin (a) and prepared by adding a caprolactone (c2) to a compound (c1) containing a plurality of active hydrogen groups.
Active hydrogen group means a group containing at least one active hydrogen atom and includes, for example, alcoholic hydroxyl group, primary amino group, secondary amino group etc. As such compounds (cl) containing a plurality of active hydrogen groups in the molecule there can be mentioned, for example,
(i) low molecular weight polyols,
(ii) linear or branched polyether polyols,
(iii) linear or branched polyester polyols,
(iv) amine compounds containing primary amino group and/or secondary amino group or hydroxyamine compounds containing, primary amino group and/or secondary amino group, and hydroxyl group, etc.
These active hydrogen group-containing compounds (c1) may have a number-average molecular weight in the range of generally 62-5,000, preferably 62-4,000 and more preferably 62-1,500. An active hydrogen group-containing compound (c1) is preferable, when it contains, as an average, at least 2 and less than 30, particularly 2-10 active hydrogen groups in the molecule.
The above-mentioned low molecular weight polyols (i) are compounds containing at least 2 alcoholic hydroxyl groups in the molecule and there can be specifically mentioned, for example, diols such as ethylene glycol, propylene glycol, 1,3-butylene glycol, 1,4-butanediol, 1,6-hexanediol, diethylene glycol, dipropylene glycol, cyclohexane-1,4-dimethylol, neopentyl glycol, triethylene glycol, hydrogenated bisphenol A etc.; triols such as glycerol, trimethylolethane, trimethylolpropane etc.; tetrols such as pentaerythritol, xcex1-methylglycoside etc.; hexols such as sorbitol, dipentaerythritol etc.; octols such as sucrose etc.
The above-mentioned linear or branched polyether polyols (ii) may have a number-average molecular weight in the range of usually 62-10,000, preferably 62-2,000 and there can be specifically mentioned, for example, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, poly(ethylene/propylene)glycol, bisphenol A polyethylene glycol ether, bisphenol A polypropylene glycol ether etc. prepared by ring-opening addition reaction of alkylene oxides (e.g., ethylene oxide, propylene oxide, butylene oxide, tetrahydro-furan etc.).
The above-mentioned linear or branched polyester polyols (iii) may have a number-average molecular weight in the range of usually 200-10,000, preferably 200-3,000 and there can be specifically mentioned, for example, products obtained by polycondensation reaction of organic dicarboxylic acid or its anhydride and organic diol under the condition of excess of organic diol. As an organic dicarboxylic acid used in this case there can be mentioned aliphatic, alicyclic or aromatic dicarboxylic acids of a carbon number 2-44, particularly 4-36, for example, succinic acid, adipic acid, azelaic acid, sebacic acid, maleic acid, fumaric acid, glutalic acid, hexachloroheptane dicarboxylic acid, cyclohexane dicarboxylic acid, o-phthalic acid, isophthalic acid, terephthalic acid, tetrahydrdophthalic acid, tetrachlorophthalic acid etc. Moreover, in addition to these dicarboxylic acids, small amount of anydride of polycarboxylic acid having more than 3 carboxyl groups, adducts of unsaturated fatty acids etc. can be used together.
As an organic diol component there can be mentioned, for example, alkylene glycols such as ethylene glycol, propylene glycol, butylene glycol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol etc., dimethylol cyclohexane etc. They may be used optionally together with small amount of polyol such as trimethylolpropane, glycerol, pentaerythritol etc.
As the above-mentioned amine compounds containing primary amino group and/or secondary amino group or hydroxy amine compounds (iv) containing primary amino group and/or secondary amino group, and hydroxyl group there can be mentioned, for example, alkylamines such as butylenediamine, hexamethylenediamine, tetraethylenepentamine, pentaethylenehexamine etc.; alkanolamines such as monoethanolamine, diethanolamine, triethanolamine, mono(2-hydroxypropyl)amine, di(2-hydroxypropyl)amine etc.; alicyclic polyamines such as 1,3-bisaminomethylcyclohexanone, isophoronediamine etc.; aromatic polyamines such as xylylenediamine, m-xylenediamine, diaminodiphenylmethane, phenylenediamine etc.; alkylenepolyamines such as ethylenediamine, propylenediamine, diethylenetriamine, triethylenetetramine etc.; other amine compounds such as piperazine and polyamide, polyamide amine, amine adduct with epoxy compound, ketimine, aldimine etc. derived from these polyamines.
Among the compounds (c1) containing a plurality of active hydrogen groups mentioned above, compounds of the above-mentioned (i), (ii) and (iv), particularly compounds selected from the group consisting of ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, diethylene glycol, hydrogenated bisphenol A, glycerol, trimethylolethane, trimethylolpropane, pentaerythritol, dipentaerythritol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, poly(ethylene/propylene)glycol, bisphenol A polyethylene glycol ether, bisphenol A polypropylene glycol ether, butylenediamine, hexamethylenediamine, monoethanolamine, diethanolamine, triethanolamine, isophoronediamine, ethylenediamine, propylenediamine, diethylenetriamine and triethylenetetramine are preferable.
On the other hand, as a caprolactone (c2) capable of adding to a compound (c1) containing a plurality of active hydrogen groups there can be mentioned xcex3-caprolactone, xcex5-caprolactone, xcex4-caprolactone etc. and particularly xcex5-caprolactone is preferable.
The above-mentioned addition reaction of a compound (c1) containing a plurality of active hydrogen groups and a caprolactone (c2) can be conducted by a per se known process. Specifically, for example, it can be conducted by heating a compound (c1) containing a plurality of active hydrogen groups and a caprolactone (c2) at about 100-about 250xc2x0 C. for about 1-about 15 hours in the presence of a catalyst like titanium compound such as tetrabutoxy titanium, tetrapropoxy titanium etc.; organic tin compound such as tin octylate, dibutyltin oxide, dibutyltin laurate etc.; metal compound such as stannous chloride etc.
The above-mentioned catalyst can be used generally in an amount of 0.5-1,000 ppm based upon the total amount of the compound (c1) containing a plurality of active hydrogen groups and caprolactone (c2). A caprolactone (c2) can be used in the range of generally 1-30 moles, preferably 1-20 moles and more preferably 1-15 moles to 1 equivalent of active hydrogen group (i.e. to 1 active hydrogen) of the compound (c1) containing a plurality of active hydrogen groups.
The polyol compounds thus obtained (c) have a high plasticizing performance based upon the compound containing a plurality of active hydrogen groups (c1), a high compatibility with epoxy resin based upon (poly)caprolactone and a high reactivity by terminal hydroxyl groups and are very useful as an internal plasticizer of an epoxy resin for paint.
Polyol compound (c) can contain the units derived from a caprolactone (c2) in the range of generally 20-95% by weight, preferably 25-90% by weight as total and can have a number-average molecular weight in the range of generally 300-10,000, preferably 400-5,000.
(d) Amino group-containing compound:
An amino group-containing compound (d) to be reacted with the aforementioned epoxy resin (a) in the present invention is a component to give the cationicity to cationize said epoxy resin by introducing amino group to the epoxy resin substrate and there is used a compound containing at least one active hydrogen which reacts with an epoxy group.
As an amino group-containing compound used for such purpose there can be mentioned, for example, mono- or di-alkylamines such as monomethylamine, dimethylamine, monoethylamine, diethylamine, monoisopropylamine, diisopropylamine, triisopropylamine, monobutylamine, dibutylamine etc.; alkanolamines such as monoethanolamine, diethanolamine, mono(2-hydroxypropyl)amine, di(2-hydroxypropyl)amine, tri(2-hydroxypropyl)amine, monomethylaminoethanol, monoethylaminoethanol etc.; alkylenepolyamines such as ethylenediamine, propylenediamine, butylenediamine, hexa-methylenediamine, tetraethylenepentamine, pentaethylenehexamine, diethylaminopropylamine, diethylenetriamine, triethylenetetramine etc. and ketiminized products of these polyamines; alkyleneimines such as ethyleneimine, propyleneimine etc.; cyclic amines such as piperazine, morpholine, pyrazine etc.
Polyol-modified Amino Group-containing Epoxy Resin
Polyol-modified amino group-containing epoxy resin used as vehicle in the paint composition of the present invention can be prepared by reacting the aforementioned epoxy resin (a) with acid compound (b), polyol compound (c) having terminal hydroxyl group derived from caprolactone and amino group-containing compound (d) by a per se known process. Reactions of acid compound (b), polyol compound (c) and amino group-containing compound (d) to the epoxy resin (a) may be conducted in an optional order. Generally, however, it is preferable to react acid compound (b) to the epoxy resin (a) first and then to add polyol compound (c) and amino group-containing compound (d) to the reaction product at the same time. It is preferable that one terminal of the polyol compound (c) adds to the skeleton of the epoxy resin (a).
Reaction of an epoxy resin (a) and an acid compound (b) can be conducted usually in an appropriate solvent and optionally in the presence of a catalyst at usually about 60-about 250xc2x0 C., preferably about 70xc2x0 C.-about 200xc2x0 C. for about 1-25 hours, preferably about 1-12 hours. As the above-mentioned solvent there can be mentioned, for example, hydrocarbons such as toluene, xylene, cyclohexane, n-hexane etc.; esters such as methyl acetate, ethyl acetate, butyl acetate etc.; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, methyl amyl ketone etc.; amides such as dimethylformamide, dimethylacetamide etc.; alcohols such as methanol, ethanol, n-propanol isopropanol etc.; and their mixtures. As a catalyst suitably used there can be mentioned, for example, titanium compounds such as tetrabutoxy titanium, tetrapropoxy titanium etc.; organic tin compound such as tin octylate, dibutyltin oxide, dibutyltin laurate etc.; metal compound such as stannous chloride etc.; organic amine compounds etc.
Thus a reaction product in which an acid compound (b) has added to the skeleton of the epoxy resin (a).
Addition reaction of a polyol compound (c) and an amino group-containing compound (d) to the reaction product can be conducted usually in an appropriate solvent as mentioned above at about 80-about 170xc2x0 C., preferably about 90-about 150xc2x0 C. for about 1-6 hours, preferably about 1-5 hours.
Ratio of usage of each reaction component in the above-mentioned reaction is not strictly limited but can be varied suitably according to the application of the paint composition etc. The following ranges, however, based upon the total solid content weight of the 4 components, epoxy resin (a), acid compound (b), polyol compound (c) and amino group-containing compound (d), are appropriate.
epoxy resin (a):
generally 60-85% by weight, preferably 62-83% by weight.
acid compound (b):
generally 0.5-15% by weight, preferably 1-10% by weight.
polyol compound (c):
generally 5-20% by weight, preferably 5-18% by weight. amino group-containing compound (d):
generally 5-25% by weight, preferably 6-19% by weight.
The polyol-modified amino group-containing epoxy resin thus prepared can have an amine value in the range of usually 30-55 mgKOH/g, preferably 32-50 mgKOH/g.
Cationic Paint Composition
The cationic paint composition provided by the present invention contains a polyol-modified amino group-containing epoxy resin prepared as mentioned above as vehicle and is preferably used in water-borne paint, particularly electrodeposition paint.
The polyol-modified amino group-containing epoxy resin according to the present invention can prepare a thermosetting cationic paint composition by using a crosslinking agent, for example, blocked polyisocyanate, melamine resin etc., particularly blocked polyisocyanate crosslinking agent in combination.
The above-mentioned blocked polyisocyanate crosslinking agent is an addition reaction product of a polyisocyanate compound and an isocyanate-blocking agent to approximately stoichiometric amount. As a polyisocyanate compound used in this case there can be mentioned, for example, aromatic, alicyclic or aliphatic polyisocyanate compounds such as tolylene diisocyanate, xylylene diisocyanate, phenylene diisocyanate, bis(isocyanatomethyl)cyclohexane, tetramethylene diisocyanate, hexamethylene diisocyanate, methylene diisocyanate, isophoron diisocyanate, diphenylmethane-2,4xe2x80x2-diisocyanate, diphenylmethane-4,4xe2x80x2-diisocyanate, polymethylene polyphenyl polyisocyanate etc.; cyclization polymers of these polyisocyanates; isocyanate-biurets; compounds containing terminal isocyanate obtained by reacting an excess amount of these isocyanate compounds with a low molecular active hydrogen-containing compound such as ethylene glycol, trimethylolpropane, hexanetriol, castor oil etc., etc. They can be used singly or in mixing 2 kinds or more.
Among them, particularly aromatic diisocyanates, above all, crude MDI is preferable.
Crude MDI is a mixture of diphenylmethane-4,4xe2x80x2-diisocyanate, diphenylmethane-2,4xe2x80x2-diisocyanate and polymethylene polyphenyl polyisocyanate as main components and there can be mentioned as commercial products Cosmonate M-50, M-200, M-100, M-300 etc. (made by Mitsui Chemicals, Inc.); Sumidur 44V10, 44V20, 44V40 etc. (made by Sumika Bayer Urethane Co., Ltd.); Lupranate M-12, M-12S, M-20, M-20S etc. (made by BASF, Germany); Mondur MR (LIGHT) etc. (made by Bayer) etc.
On the other hand, the aforementioned isocyanate blocking agent is a substance to be added to an isocyanate group of a polyisocyanate compound and to block it and the blocked polyisocyanate compound formed by the addition is desirably stable at normal temperature and capable of reproducing a free isocyanate group, dissociating the blocking agent, at the time of being heated to a baking temperature (usually about 100-about 200xc2x0 C.) of the coating film. As a blocking agent meeting such requirements there can be mentioned, for example, lactam type compounds such as xcex5-caprolactam, xcex3-butyrolatam etc.; oxime type compounds such as methyl ethyl ketoxime, cyclohexanone oxime etc.; phenol type compounds such as phenol, p-t-butylphenol cresol etc.; aliphatic alcohols such as n-butanol, 2-ethylhexanol etc.; aromatic alkyl alcohols such as phenylcarbinol, methylphenylcarbinol etc.; ether alcohol type compounds such as ethylene glycol monobutyl ether, diethylene glycol monoethyl ether etc.
Compounding ratio of a polyol-modified amino group-containing epoxy resin and a blocked polyisocyanate crosslinking agent can be in the range of genarally 55-90% by weight, preferably 60-85% by weight and more preferably 60-80% by weight of the polyol-modified amino group-containing epoxy resin and genarally 10-45% by weight, preferably 15-40% by weight and more preferably 20-40% by weight of the blocked polyisocyanate crosslinking agent based upon the total solid content weight of both components.
The cationic paint composition of the present invention containing the above-mentioned polyol-modified amino group-containing epoxy resin and a blocked polyisocyanate crosslinking agent can be prepared, for example, by sufficiently mixing the polyol-modified amino group-containing epoxy resin and the blocked polyisocyanate crosslinking agent and then water-solubilization or water-dispersing said epoxy resin through neutralization with a water-soluble organic carboxylic acid usually in an aqueous medium. As an organic carboxylic acid for neutralization particularly acetic acid, formic acid or their mixture are preferable. By using these acids finishing property, throwing power and low temperature curability of the formed paint composition and stability of the paint are improved.
In the paint composition of the present invention a bismuth muth compound can be contained as anticorrosive agent. There is no restriction in the kind of bismuth compound to be compounded and there can be mentioned, for example, inorganic bismuth compounds such as bismuth oxide, bismuth hydroxide, basic bismuth carbonate, bismuth nitrate, bismuth silicate etc. Among them particularly bismuth hydroxide is preferable.
Moreover, it is possible to use, as a bismuth compound, an organic bismuth salt which is prepared by reacting a bismuth compound as mentioned above and more than 2 kinds of organic acids, at least one of which is an aliphatic hydroxycarboxylic acid. As an organic acid usable for the preparation of said organic bismuth salt there can be mentioned, for example, glycolic acid, glyceric acid, lactic acid, dimethylolpropionic acid, dimethylolbutyric acid, dimethylolvaleric acid, tartaric acid, malic acid, hydroxymalonic acid, dihydroxysuccinic acid, trihydroxysuccinic acid, methylmalonic acid, benzoic acid, citric acid etc.
The above-mentioned inorganic bismuth compounds and organic bismuth salts can be used each singly or in combination of more than 2 kinds.
Content of these bismuth compounds in the paint composition of the present invention is not strictly limited but can be varied in a wide range according to the performances required to the paint etc. Usually, however, less than 10% by weight, preferably the range of 0.05-5% by weight, based upon the resin solid content in the paint composition of the present invention, is appropriate.
The cationic paint composition of the present invention can further contain, optionally, a tin compound as a curing catalyst. As said tin compound there can be mentioned, for example, organotin compounds such as dibutyltin oxide, dioctyltin oxide etc.; aliphatic or aromatic carboxylates of dialkyltin such as dibutyltin dilaurate, dioctyltin dilaurate, dibutyltin diacetate, dioctyltin dibenzoate, dibutyltin dibenzoate etc. Among them, dialkyltin aromatic carboxylates etc. are preferable from the viewpoint of low temperature curability.
The content of such a tin compound in the paint composition of the present invention is not strictly prescribed but can be varied in a wide range according to the performances required to the paint etc. The tin content, however, is preferably in the range of usually 0.01-8 parts by weight, preferably 0.05-5.0 parts by weight per 100 parts by weight of the resin solid content in the paint.
In the cationic paint composition of the present invention there can be further compounded, as necessary, additives for paint such as color pigment, extender pigment, anticorrosive pigment, organic solvent, pigment dispersing agent, surface adjustment agent etc.
The cationic paint composition of the present invention can coat the surface of a desired substrate by cationic electrodeposition coating. The electrodeposition coating can be conducted generally in an electrodeposition bath comprising the paint composition of the present invention diluted with deionized water etc. to the solid content concentration of about 5-about 40% by weight, preferably 15-25% by weight and adjusted its pH in the range of 5.5-9 under the condition of the bath temperature usually adjusted to about 15-about 35xc2x0 C. and the load voltage of 100-450V.
The film thickness of the electrodeposition coating film formed by using the paint composition of the present invention is not particularly limited but is preferable generally in the range of 10-45 xcexcm, particularly 15-30 xcexcm based upon a cured coating film. The baking temperature of the coating film is suitable generally in the range of about 120-about 200xc2x0 C., preferably about 140-about 180xc2x0 C. at the surface of the substrate. The baking time can be about 5-60 minutes, preferably about 10-30 minutes.
The cationic paint composition of the present invention can be used preferably as cationic electrodeposition paint. Besides it can also be used as solvent type paint as an anticorrosive primer for a steel plate to be coated by means of electrostatic coating, roller coating etc.
Furthermore, the paint composition of the present invention can be used as two liquid type room temperature-drying paint using polyisocyanate compound or melamine resin as crosslinking agent or adhesive.
The cationic paint composition of the present invention forms a cured coating film excellent in corrosion resistance, rust preventive steel plate aptitude and adhesion to the substrate and is useful, for example, as undercoat paint for car body, car parts, in the field of construction and architecture etc.
Especially, to a cationic electrodeposition paint, a throwing power is required as a rust preventive countermeasure for baggy parts of a car body (locker, side-sill, pillar), and a higher throwing power is required because of more complicated body structure such as putting reinforcement to the locker part and in the side-sill from the recent levelling up of safety level.
The cationic paint composition of the present invention has a high throwing power and can form an electrodeposition coating film excellent in corrosion resistance with excellent electrodeposition coating aptitude even for a car body with complicated structure.
Then the present invention will be described more specifically by referring to examples. The present invention shall, however, not be restricted to these examples in any way. xe2x80x9cPartxe2x80x9d and xe2x80x9c%xe2x80x9d means xe2x80x9cpart by weightxe2x80x9d and xe2x80x9c% by weightxe2x80x9d, respectively.